The present invention is generally related to deflection yokes for cathode ray tube (CRT) displays and, more particularly, to a very wide angle deflection yoke for use with a small gun-base, in-line CRT display system.
Examples of prior art deflection systems to which the invention is related are disclosed in U.S. Pat. Nos. 3,430,099 issued to R. B. Ashley, 2,925,542 issued to R. B. Gethman, 4,217,566 issued to Eizaburo Hamano, and 4,143,346 issued to S. R. Borkar. Ashley discloses a deflection system in which self convergence of vertical lines is produced by outside electron beams. Gethman teaches the analytical discription of deflection yoke windings. Hamano teaches pin cushion correction by means of permanent magnets. Borkar teaches the use of segmented saddle type windings in a combination with a toriodal yoke.
As evidenced by the foregoing, it is well known how deflection in a CRT display is accomplished. Basically, two sets of magnetic poles, orthogonally aligned to each other and having simple winding distributions, are required to accomplish the deflection function. The general principles of the design of deflection coils are presented in Chapter 18 entitled "Deflection Coils" in Television Engineering by A. M. Dhake, McGraw-Hill (1979). In my prior U.S. Pat. No. 4,117,434, I disclosed a hybrid deflection system for a CRT in which toroidal-type quadripolar correction coils, having areas vacant of any windings within the coils, lie wound in accordance with a Fourier series winding distribution on a split ring magnetic core of the deflection system comprising saddle-type horizontal deflection coils and toroidal-type vertical deflection coils. The winding distribution of such non-distorting deflection coils is given by the following equation: EQU n(.theta.-.beta.)=NA.sub.1 sin(.theta.-.beta.) (1)
where n(.theta.-.beta.) represents the number of turns of wire encompassed by the angle (.theta.-.beta.) in a quadrant of the core between the X and Y axes, N is the total number of windings in th quadrant, and A.sub.1 is the Fourier coefficient. .theta. varies from 0.degree. to 180.degree. for horizontal coils and from 90.degree. to 270.degree. for vertical coils. For the horizontal case, for example, when .theta.=90.degree., n=N, and when .theta.=180.degree., n=0. .beta.=0.degree. for horizontal coils, and .beta.=90.degree. for vertical coils. The deflection winding distribution can be designed to effect convergence of off-axis (outside) beams when the winding distribution obeys the following equation: EQU n(.theta.-.beta.)=N[A.sub.1 sin(.theta.-.beta.)+A.sub.3 sin(3.theta.-.beta.)+A.sub.k sin(k.theta.-.beta.)] (2)
where A.sub.1, A.sub.3 . . . A.sub.k are Fourier coefficients. The on-axis (center) beam can be made to converge with the off-axis beams by use of magnetic shunts in the CRT when the result of converging off-axis beams is a center beam convergence error. If the winding distribution is a constant throughout the coil, means for pincushion distortion correction, external to the deflection coils, may be required. This is always true in the case of left and right pincushion correction since the vertical coil winding distribution coefficient, A.sub.3, is positive for pincushion correction and negative for self convergence.
Winding distributions can be made variant with axial position so that the distributions are given by the following equation: EQU n(z,.theta.-.beta.)=N[A.sub.1 (z)sin(.theta.-.beta.)+A.sub.3 (z)sin(3.theta.-.beta.)+A.sub.k (z)sin(k.theta.-.beta.)] (3)
where z is the length along the CRT axis. This is convenient since display distortions are related to the axial position at which particular winding distributions occur. The general fact of these relationships has been well known to those practiced in the field and was formalized by Kaashoak in his thesis entitled "A Study of Magnetic-Deflection Errors", Techinical University Eindhoven, July 1968, N. V. Philips Research Reports.
Those working at Toshiba and Hitachi demonstrated that actual winding distributions can be functionally altered by use of magnetic shunts adjacent to the winding. See for example "Deflection Yoke for Dynamic Raster Distortion Correction Free Color Picture Tube", Toshiba New Product Information, and "Pincushion Distortion-Free Self-Convergence Deflection System", by Takesuke Maruyama et al, Hitachi, Ltd., Tokyo, Japan. Phillips has used segmented windings to achieve particular saddle coil distributions starting with 25V displays having delta gun configurations. Toshiba has produced yokes in which the low frequency magnetic field external to the yoke is collected and redirected to correct pincushion. Using these techniques and that of CRT magnetic shunt use, self converging, pincushion correcting deflection systems have been designed. These systems worked well with gun bases as small as 6.6 mm and deflection angles as large as 100.degree.. However, there has been difficulty in reaching 110.degree. deflection angles with the prior art systems.